Compliant plate seals for turbomachinery

ABSTRACT

A shaft seal serves to reduce leakage between a rotating shaft and a static shell. The shaft seal includes a plurality of compliant plate members, each having a root and a tip. The compliant plate members are secured to the static shell at their root in facing relation. The tips of the compliant plate members define a sealing ring between the static shell and the rotating shaft. An axial flow resistance member is disposed within the compliant plate members and serves as a barrier to axial leakage flow between the compliant plate members.

This application is a continuation of U.S. patent application Ser. No.11/504,061, filed Aug. 15, 2006, now U.S. Pat. No. 7,419,164, the entirecontents of which are hereby incorporated by reference in thisapplication.

BACKGROUND OF THE INVENTION

The invention relates to a sealing structure between a rotatingcomponent and a static component and, more particularly, to a compliantplate seal arrangement that additionally utilizes features of alabyrinth seal.

Dynamic sealing between a rotor (e.g., rotating shaft) and a stator(e.g., static shell or casing) is an important concern inturbomachinery. Several methods of sealing have been proposed in thepast. In particular, sealing based on flexible members has been utilizedincluding seals described as leaf seals, brush seals, finger seals, shimseals, etc.

A brush seal is comprised of tightly packed generally cylindricalbristles that are effective in preventing leakage because of theirstaggered arrangement. The bristles have a low radial stiffness thatallows them to move out of the way in the event of a rotor excursionwhile maintaining a tight clearance during steady state operation. Brushseals, however, are effective only up to a certain pressure differentialacross the seal. Because of the generally cylindrical geometry of thebristles, the brush seals tend to have a low stiffness in the axialdirection, which limits the maximum operable pressure differential togenerally less than 1000 psi.

To overcome this problem, leaf seals have been proposed that include aplate-like geometry with higher axial stiffness and therefore thecapability of handling large pressure differentials (an exemplaryconventional leaf seal is illustrated on the left side of FIG. 1). Axialleakage, however, remains a problem due to the leaf seal geometry. Thatis, if the leaves are packaged tightly close to the rotor, there will begaps at the leaf roots since the seal is curved, which gaps potentiallycause leakage and in turn offset the benefits of the seal.

BRIEF DESCRIPTION OF THE INVENTION

In an exemplary embodiment of the invention, a shaft seal reducesleakage between a rotating shaft and a static shell. The shaft sealincludes a plurality of compliant plate members attached in facingrelation to the static shell, where the compliant plate members define asealing ring between the static shell and the rotating shaft. Each ofthe compliant plate members includes at least one slot therein. Theshaft seal also includes at least one static ring attached to the staticshell and extending radially into the at least one slot in the compliantplate members.

In another exemplary embodiment of the invention, the shaft sealincludes a plurality of compliant plate members, each having a root anda tip, where the compliant plate members are secured at their roots infacing relation to the static shell. The tips of the compliant platemembers are arranged circumferentially about the rotating shaft. Anaxial flow resistance member is disposed within the compliant platemembers and serves as a barrier to axial leakage flow between thecompliant plate members.

In still another exemplary embodiment of the invention, the shaft sealincludes a plurality of compliant plate members attached in facingrelation to the stator, the compliant plate members defining a sealingring between the stator and the rotor. Each of the compliant platemembers includes a plurality of varying length slots therein. Acorresponding plurality of static rings are attached to the stator andextend radially into the plurality of slots in the compliant platemembers, respectively. The plurality of static rings have varying radiallengths corresponding to the varying length slots and serve as a barrierto axial leakage flow between the compliant plate members.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view showing a side-by-side comparison of aconventional leaf seal (left) to one embodiment of a compliant plateseal described herein (right);

FIG. 2 is a perspective view of the compliant plate seal shown in FIG.1; and

FIGS. 3 and 4 show alternate shapes for the complaint plate members.

DETAILED DESCRIPTION OF THE INVENTION

The improved compliant plate seal described herein achieves a structurethat curtails the above-mentioned axial leakage seen in a conventionalleaf seal by employing a geometry that includes features of a labyrinthseal. As noted, in a conventional leaf seal, because the leaves arepacked tightly at the tips and loosely at the roots, axial leakageentering the leaf pack tends to flow/expand radially outward, thenaxially and finally converges as it exits the leaf pack.

With reference to FIGS. 1 and 2, a shaft seal 10 serves to reduce axialleakage between a rotor 12, such as a rotating shaft, and a housing 14,attached to the turbine static shell 15. The shaft seal 10 is providedwith a plurality of compliant plate members 16 secured at their roots infacing relation (i.e., face-to-face) to the housing 14. The compliantplate members 16 define a sealing ring between the housing 14 and therotating shaft 12.

An axial flow resistance member 17 is disposed within the compliantplate members 16 and serves as a barrier to axial leakage flow betweenthe compliant plate members 16. In a preferred arrangement, the axialflow resistance member 17 includes at least one ring 18 attached to thehousing 14 and extending radially into a corresponding at least onecircumferential slot 20 in the compliant plate members 16. As depictedin FIGS. 1 and 2, each of the compliant plate members 16 preferablyincludes multiple slots 20 that can be of varying radial lengths andaxial widths, and the axial flow resistance member 17 includes acorresponding multiple rings 18 of corresponding radial lengths,respectively. Although three rings and slots are shown in FIG. 1, thisdepiction is exemplary, and the invention is not meant to be limited. Ina broader sense, in some applications, adjacent ones of thecircumferential slots 20 comprise different radial lengths with thestatic rings 18 extending radially into the circumferential slots 20.

Although the illustrated slots 20 are shown having a rectangular shape,those of ordinary skill in the art will appreciate that other shapedslots may be utilized. The slots 20 may also be formed in differentwidths and varying lengths. Other compliant plate shapes may also besuitable, such as T-shaped, trapezoidal, and the like as shown in FIGS.3 and 4.

The rings 18 force the leakage flow to follow a more tortuous path,thereby increasing the resistance to leakage flow. The configurationthus mimics a labyrinth seal within a compliant plate seal. The leavesretain their bending flexibility and axial stiffness, which areimportant for the seal functionality.

Since the compliant plates are packed more tightly at the tips (adjacentthe rotor) than at the roots (adjacent the stator), the rings 18 neednot extend radially from the plate root all the way to the plate tip.Rather, the rings 18 need only extend into a portion of the compliantplates 16 as shown.

An important advantage of compliant plate seals is a pressure build-upeffect that is generated upon rotor rotation. The effect causes thecompliant plates 16 to lift during rotor rotation. In response to thislift, any other pressure forces, and compliant plate materialelasticity, an equilibrium state is attained for each compliant platethat leaves a very small clearance between the plate tips and the rotor12. This small clearance between the plate tips and the rotor reducesfrictional heat generation by minimizing or eliminating physicalcontact.

Although a housing 14 is shown in the figures and described above,compliant plates 16 and rings 18 may directly be integrated with thestator 15, depending on the application. An intermediate housing may benecessary only for practical purposes such as assembly and fabricationand not for functionality. Additionally, although front and back rings22, 24 are shown in the figures, the proposed configuration with therings disposed within the compliant plates should achieve the desiredobjective without a need for front and back rings. In addition to thedescribed features, the front and back rings can also be added to theseal. Typically, the front and back rings 22, 24 will be part of thehousing as shown in FIG. 1.

The figures show a stator that is external to a rotor. In anotherarrangement, the rotor can be external to the stator.

The compliant plates may be coated with special materials to achieve oneor more of the following objectives (without limitation): minimizefriction, wear and heat generation in case of relative sliding, act asdiffusion barrier, and allow high temperature operation. The surface ofthe rotor, which is in close proximity to the compliant plate tips mayalso be coated for the above or other reasons. Common coating methodsinclude Physical Vapor Deposition, thermal spray and galvanicdeposition, to name a few. Coating materials include, but are notlimited to, Titanium Nitride, Zirconium Nitride,NickelChrome-ChromeCarbide along with solid lubricants, Nickel, etc.

The shaft seal described herein provides a high-pressure dynamic sealbetween a rotating component and a static component. The seal includesmultiple compliant plates that comply in the event of rotor excursionbut are very stiff along the direction of pressure drop. Incorporationof an axial flow resistance member forces the axial flow to follow atortuous path at the seal root. A combination of tightly packed sealtips and flow obstructing features at the seal root results in asignificantly reduced axial leakage.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiments,it is to be understood that the invention is not to be limited to thedisclosed embodiments, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1. A shaft seal for reducing leakage between a rotating shaft and astatic shell, the shaft seal comprising: a plurality of compliant platemembers attached in facing relation at root ends to the static shell,the compliant plate members defining a sealing ring between the staticshell and the rotating shaft, wherein each of the compliant platemembers comprises at least one slot therein extending radially into thecompliant plate member through a radially outwardmost edge of the rootend; and at least one static ring attached to the static shell andextending radially into the at least one slot in the compliant platemembers, each of the at least one static ring extendingcircumferentially through and between a plurality of the compliant platemembers such that the at least one static ring serves as a barrier to atleast some axial leakage flow between the compliant plate members.
 2. Ashaft seal according to claim 1, wherein the compliant plate members areattached to the static shell via a housing.
 3. A shaft seal according toclaim 2, wherein the at least one static ring is integrated with thehousing.
 4. A shaft seal according to claim 1, wherein the compliantplate members are rectangular shaped.
 5. A shaft seal according to claim1, wherein the compliant plate members are T-shaped.
 6. A shaft sealaccording to claim 1, wherein the compliant plate members are trapezoidshaped.